This disclosure relates to mitigating effects of electromagnetic interference (“EMI”), also known as radio frequency interference (“RFI”), in integrated circuits. Particularly, this disclosure relates to providing an EMI shield in relation to integrated circuit devices.
EMI is disturbance that can degrade or limit the performance of an electrical circuit affected by it. Sources of EMI that may affect a circuit include any object that carries rapidly changing electrical currents. Effectively immunizing a particular device from electromagnetic radiation from an external EMI source, and effectively avoiding damaging or undesirable radiation from a particular device, may require use of an EMI shield. That is, an EMI shield may serve one or both of two purposes: it may be installed over a particular component to shield that component from effects of radiation from sources external to the component; and it may be installed over a particular component to prevent radiation originating in the particular component from affecting surrounding components or devices.
Integrated circuit (“IC”) device components, such as ICs used in portable electronics devices such as cell phones, and in electronic equipment, including home entertainment equipment and computers, can be sources of unwanted electromagnetic signals. A portable electronic device such as a cell phone typically contains several IC components (which may be IC chips, IC chip packages, or IC package modules) coupled onto a circuit board, and some of these components may generate EM signals that interfere with the operation of other components in the device. EMI shielding may be required to protect circuitry in an electronic component from a source external to the component (including other electronic components.
In one approach to protecting components from EMI, shielding can be constructed over the components. The shield is constructed of an electrically conductive material such as sheet metal (which may be perforated) or metal screen, electrically coupled to a reference potential, which may be ground, for example. It is typically formed as a box installed over the component to be shielded and soldered to contact points on the circuit board surrounding the component. Alternatively, a frame may be soldered to contact points on the circuit board, and a sheet metal cover may be snap-coupled to the frame over the component. Undesirably, such a shield adds weight and bulk (thickness, length and width) to the device in which it is used.
In another approach to constructing a shield, layers of material are applied onto the circuit board and the components: a first layer provides waterproofing or water resistance, and is of a non-conductive material; and a second layer, applied over the first, is of a conductive material and provides EMI shielding. Contact pads on the circuit board are exposed by openings through the first layer, and the second layer is electrically coupled to the contact pads.
EMI shields as disclosed herein are formed by application of the shield material where it is needed to provide the desired shielding effect. Accordingly less of the shielding material is required than would be deployed in a configuration in which the component is fully covered by the shield material, or in a configuration in which the shield material is applied fully over a broad area including the components and then removed in part from areas where it is not needed, or otherwise to form openings (as in “subtractive” processes). Moreover, because the topside of the component is applied as a grid, the shield can be “tuned” to selectively block or allow passage (admission or transmission) of frequencies in various ranges and/or in ranges of various widths in the electromagnetic spectrum. Depending upon the functionality of the particular component, or upon the functionalities of particular regions within the component, it may be desirable to “tune” one or more areas of the component surface differently than others.